The present invention relates to a flight management assembly of an aircraft, in particular of a passenger or cargo transport aircraft, and to a method for monitoring guidance instructions generated by such a flight management assembly.
Although not exclusively, the present invention applies more particularly to an aircraft implementing operations of the RNP AR (Required Navigation Performance with Authorization Required) type. These RNP AR operations are based on area navigation of the RNAV (aRea NAVigation) type and on operations with required performance of the RNP (Required Navigation Performance) type. They have the distinctive feature of necessitating special authorization in order to be able to be used on an aircraft.
It is known that the RNP concept corresponds to area navigation to which is added, (on board the aircraft) monitoring and warning means which make it possible to ensure that the aircraft remains in a corridor, called RNP, around a reference trajectory. Outside of this corridor, potentially there is relief, e.g., a mountain, or other aircraft. The required performance for an RNP type operation is defined by an RNP value which represents the half-width, in nautical miles (NM), of the corridor around the reference trajectory, within which the aircraft must remain for 95% of the time during the operation. A second corridor (around the reference trajectory) having a half-width of twice the RNP value is also defined. The probability of the aircraft going outside of this second corridor must be less than 10−7 (10 to a power of the minus seventh) per hour of flight.
The concept of RNP AR operations is even more restrictive. The RNP AR procedures are, in fact, characterized by:
(i) RNP values: that are less than or equal to 0.3 NM on approach and which can drop down to 0.1 NM; and which are strictly less than 1 NM at the start of and during a go-around, and which can also drop down as far as 0.1 NM;
(ii) a final approach segment which can be curved; and
(iii) obstacles (mountains, traffic, etc.) which can be situated at twice the RNP value with respect to the reference trajectory whereas, for the usual RNP operations, an additional margin with respect to obstacles is provided.
Air traffic authorities have defined a target safety level TLS (Target Level of Safety) of 10−7 per hour of flight. In the case of RNP AR operations, as the RNP values can drop down to as low as 0.1 NM and the obstacles can be situated at twice the RNP value from the reference trajectory, this objective is represented by a probability of the aircraft leaving the corridor of half-width D=2·RNP which must not exceed 10−7 per hour of flight.
The present invention applies to a flight management assembly comprising guidance systems, each provided with a flight management system of the FMS (Flight Management System) type.
The items of equipment installed on board an aircraft, and notably the flight management assembly, must make it possible to achieve the target level of safety if the aircraft must implement operations with required navigation performance with authorization required of the RNP AR type.
The objective is to have the capability of flying the RNP AR procedures with RNP values down to 0.1 NM and to do so without restriction (in a normal situation and in the case of a failure) during departure, approach and go-around.
In order that an aircraft may have the capability of flying such RNP AR procedures, it is notably necessary to be able to eliminate an erroneous source of computation of guidance commands (or instructions) from the guidance loop, in order to counter its possible effects on the trajectory of the aircraft.
In order to be able to implement an operation of the RNP 0.1 type, the flight management assembly must make it possible to comply with a severity of the “hazardous” (dangerous) type in the case of loss of or error in the guidance commands. Moreover, it is necessary, in the case of detection of an incorrect computation, that the aircraft can continue to be guided automatically in order to be kept inside the RNP corridor.
With a flight management assembly having two flight management systems, in the case of disagreement between the two flight management systems, the assembly is not capable of identifying the one that is defective, and the aircraft can therefore no longer be guided automatically and is not capable of implementing such RNP operations.